In the 1950's and '60's, a number of communities laid steel-reinforced concrete pipes for their main sewer lines, expecting them to be durable enough to last virtually forever. Recently, communities are finding that these pipelines have deteriorated significantly. It is only now being discovered that sulfide gases in sewage chemically attack the lime in concrete and corrode a small portion of the pipe each year. In some cases, sulfide gases rise out of the sewage and concentrate at the upper inner surfaces of the pipe, accelerating the deterioration of the upper surface. Once the concrete has deteriorated, the sulfide gases and sewage corrode the steel reinforcements. At some point, the pipeline can become so weakened as to collapse. Portions of the pipe crown fall into the flow conduit and sink to the bottom, where they obstruct the flow of sewage. Structures above the pipeline may then collapse with the undermined soil over the outfall line, potentially cutting off the entire fluid flow. Even if the pipeline does not collapse, it may leak raw sewage in the surrounding ground, potentially polluting ground water sources.
The existing method of large pipe restoration is limited to unearthing the pipe and replacing deteriorated portions or, in some cases, the entire pipeline. The cost of unearthing old pipe and laying in a new pipe is enormous, in addition to the expense of constructing a temporary sewage system. In some cases, it is not possible to access the pipeline from above ground, because buildings and other structures have been built on top of the pipeline (in the expectation that the pipeline would never need repair). Either the structure must be removed, or the pipeline must be approached horizontally, by digging under the building. Either case requires additional time and expense. Since existing main sewer lines are typically many miles long, there could be a considerable number of such structures. Therefore, not only is the cost of restoring new pipe expensive (especially steel-reinforced concrete pipe), but also in highly populated areas, it can be very disruptive and time consuming.
There exist several pipe restoration methods for small diameter pipes (24 inches and smaller). However, these methods require by-pass pumping, thus requiring the operations line to be taken out of service. Arrangements for service re-connections must be coordinated while rehabilitating the line. These methods include: in-situ form where an existing pipeline is lined with an impregnated fiberglass thermopolyester rest sock; pipe-within-a-pipe where a PVC pipe is pre-shrunk and heated to form an interior wall within an existing pipeline; U-liner method where a polyethelene pipe is formed inside an existing pipeline using steam; and, installing pipe sections method where hydraulic cylinders having sectional insertion components, install pipe sections consisting of PVC, steel, polyethelene, etc. within the out-of-service line.
For small-diameter pipes, it is currently known to restore an existing pipeline by pushing rigid pipe sections into the existing pipeline, end-to-end, without having to take the line out of service. First, the existing pipeline is cleaned, or at least cleared, of obstructing debris. Next, a pipe insertion machine pushes rigid new pipe sections, typically fabricated of steel, plastic, or other suitable material, into the existing pipeline. The new sections are pressed intermittently into the pipeline by means of a hydraulic ram. The new pipe section may be shoved in at an existing pipe opening (i.e., a manhole) or an opening may be created by unearthing a portion of the pipe and cutting a coupon from its upper surface.
In general, pipe diameters of 30 inches and larger cannot be periodically taken out of service for repairs, due to the large flow volumes and connecting trunk outfalls. Therefore, the above by-pass pumping methods are not viable options. The insertion method above is not available either for use with large diameter pipes due to the lack of an insertion machine powerful enough to push a large pipe train. The most powerful known pipe insertion machine provides only about 100 tons of axial force. For the large diameter pipes (over 7 feet), upwards of 300 to 500 tons of axial force are needed. Current machines may not easily be resized for the proportions of large-diameter pipes, because many of the components are not produced in larger sizes. If the components were available, the resulting machine would be quite slow, because existing designs have power transmission methods that limit the axial load capability (i.e., the translational power is provided directly from the hydraulic power.) For these reasons, the pipe insertion method of pipeline restoration has not hereto been available for use with Very large diameter pipes.
Thus, a need exists for a pipe insertion machine that may be used to safely control large diameter pipe insertion into a high flow existing pipeline environment. The ideal pipe insertion machine should be powerful enough to quickly push large-diameter new pipe sections into an existing pipeline without disrupting flow or altering the environment of the collection network. The present invention is directed to fulfilling this need.